R3303-HP HSR6800 Routers Layer 3 - IP Services Configuration Guide

Dynamic ARP entry

ARP automatically creates and updates dynamic entries. A dynamic ARP entry is removed when its aging

timer expires or the output interface goes down, and it can be overwritten by a static ARP entry.

Static ARP entry

A static ARP entry is manually configured and maintained. It does not age out, and cannot be overwritten

by a dynamic ARP entry.

Static ARP entries protect communication between devices, because attack packets cannot modify the

IP-to-MAC mapping in a static ARP entry. The device supports only short static ARP entries.

Static ARP entries can be classified into long, short, and multiport ARP entries.

To configure a short static ARP entry, you only need to specify the IP address and MAC address.

• If the output interface is a Layer 3 Ethernet interface, the short ARP entry can be directly used to

forward matching packets.

• If the output interface is a VLAN interface, the device first sends an ARP request whose target IP

address is the IP address of the short entry. If the sender IP and MAC addresses in the received ARP

reply match the IP and MAC addresses of the short static ARP entry, the device adds the interface

receiving the ARP reply to the short static ARP entry, and then uses the resolved entry to forward the

matching IP packets.

To communicate with a host by using a fixed IP-to-MAC mapping, configure a short static ARP

entry on the device.

NOTE:

The device does not respond to an ARP request that contains the sender IP in a static mappin

but the

sender MAC address is not in the mapping.

Configuring a static ARP entry

A static ARP entry is effective when the device works correctly. If a VLAN or VLAN interface is deleted,

all resolved short static ARP entries in the VLAN becomes unresolved.

To configure a static ARP entry:

Step Command Remarks

1. Enter system view.

system-view N/A

2. Configure a short

static ARP entry.

arp static ip-address mac-address [ vpn-instance

vpn-instance-name ]

By default, no short static ARP

entry is configured.

Configuring the maximum number of dynamic ARP

entries for an interface

An interface can dynamically learn ARP entries, so it might hold too many ARP entries. To solve this

problem, you can set the maximum number of dynamic ARP entries that an interface can learn. When the

maximum number is reached, the interface stops learning ARP entries.